Synthetic filament



Patented Dec. 31, 1940 UNITED STATES PATENT OFFICE SYNTHETIC FILAMENT No Drawing. Application November 10, 1937, Serial No. 173,943

18 Claims.

This invention relates to artificial filaments,

bristles, and the like, and more particularly to an improvement in the preparation of such articles from synthetic linear condensation polyamides.

This application is a continuation-in-part of my application Serial Number 125,925, filed February 15, 1937.

The materials described herein for making improved bristles are thefiber-forming linear con- 2,071,253 and 2,190,770. These polymers are microcrystalline and can be formed into various useful articles such as filaments, ribbons, sheets, etc. A characteristic property of filaments and the like prepared from such polymers is that they are converted under application of stress in the solid state, herein referred to as colddrawing, into oriented products of greater utility. The cold-drawn articles show definite orientation along the fiber axis whereas the undrawn products are usually substantially unoriented. For most purposes, the oriented filaments are more useful than the unoriented filaments since they are tougher and have better elastic recovery. Of this new class of fiber-forming materials, the polyamides form a particularly valuable sub-class. It is with this class of polymers that the present invention is concerned. Linear condensation polyamides are of two types, those derived from suitable diamine-dibasic acid mixtures or their equivalents, and those derived from polymerizable monoaminomonoearboxylic acids or their amide-forming derivatives. It will be noted that the linear condensation polyamides are derived from bifunctional polyamide-forming reactants.

While the properties of the synthetic linear condensation polyamides will of course vary somewhat with the nature of the reactants used in their preparation and with the extent to which they have been polymerized, common characteristics of oriented filaments and the like derived therefrom are high tenacity both wet and dry, high degree of orientation, extraordinary resistance to solvents and chemical reagents, exceptionally good elastic recovery, good dyeing properties, and resistance to hydrolysis under conditions encountered in service. When heated 50 with strong mineral acids, however, the filaments are hydrolyzed to the monomeric reactants from which they were derived.

A valuable property of the polyamides is that they can be formed into shaped articles such as filaments, ribbons, etc., directly from melt. When densation polymers described in Patents 2,071,250,

the articles so formed have a small diameter as in the case of filaments to be usedv in making fibers for fabric manufacture, no dimculty is encountered in cold-drawing the filaments. However, when it is desired to prepare large colddrawn filaments such as the bristles with which the present invention is concerned, the diameter of which after cold-drawing is usually from 0.003 to 0.06 inch, the force required to draw the large filaments at the ordinary speed of drawing is often suflicient to break the filaments rather than cold-draw them, unless they have been prepared or pretreated in a suitable manner as more fully described below.

Methods for successfully cold-drawing the.

method described in the second mentioned patent the filament spun from the molten polyamide by extrusion through a suitable spinneret is rapidly chilled, preferably .with the use of a liquid nonsolvent. This rapid cooling or quenching gives a tougher and more readily drawable product than is obtained by cooling the filament slowly, e. g., with the use of air. A convenient method for accomplishing this quenching or tempering" is to spin the filament directly into water or other liquid medium which does not dissolve the filament. The quenched filament obtained in this way can usually be cold-drawn directly, but this operation is facilitated by further soaking the filament, as described in the first mentioned patent, before cold-drawing. The present invention is concerned with the after treatment or conditioning of the cold-drawn bristle.

Large oriented polyamide filaments prepared by the above methods have properties which make them useful as bristles. They are strong, tough, have good stiffness, good snap, and exhibit reasonably good recovery from deformation both wet and dry. Although these large oriented filaments can be used directly as bristles in the preparation of brushes, I have now found that their utility for this and other purposes can be greatly increased by the process of my invention described below. As will be shown, this process greatly increases the ability of the bristles to recover from deformation. It also improves their wearing qualities or life in service.

An object of this invention therefore is to prepare synthetic filaments of improved properties. More specific objects are to improve the properties of large oriented filaments of synthetic polyamides for use as bristles. Another object is to prepare synthetic bristles which are superior to natural bristles in their ability to recover from deformation and in their resistance to wear. Other objects will become apparent as the description proceeds.

These objects are accomplished by treating with water, in the manner more fully pointed out below, an oriented filament, particularly a bristle, formed by cold-drawing a filament derived from a synthetic linear condensation polyamide.

I have found that when oriented polyamide bristles are treated, preferably in a straight position and before they are fabricated into a brush, with hot water or steam, until the bristles exhibit at least 15% better recovery from deformation, and then dried in a straight position, bristles are obtained which are markedly superior to untreated bristles. By virtue of this improvement in recovery brushes prepared from these bristles have much longer life in service than those prepared from untreated bristles.

Before describing the water after-treatments in detail, reference should be made to the tests used in determining the stiffness, recovery, and wearing qualities of bristles. The stiffness of the bristles was determined by placing a bristle across two supports, one inch apart, applying a known weight on the bristle midway between these supports and observing with a traveling microscope the deflection of the bristle one minute after the weight was applied. From the value of this deflection, the intrinsic stiffness of the bristle in terms of modulus of elasticity (E) is determined by means of the following equation:

where W is the weight in pounds, I is the length in inches between the supports, D is the diameter of the bristle in inches, and Ya is the deflection of the center of the bristle in inches. This method of expressing stiffness makes it possible to compare the stiffness of bristles of different diameters. Since for the apparatus used in the tests herein described, I was one inch, W was 0.00136 lb. (0.6175 g.), and the deflection was measured in millimeters, the formula becomes where D is in inches and Ye in millimeters. The reciprocal of the deflection itself is a measure of the stiffness, and it is evident from the equation that for bristles having the same modulus of elasticity (E), the stiffness of a bristle increases as the fourth power of its diameter. It follows therefore that a slight increase in the diameter of a bristle results in a tremendous increase in stifl'nms.

The recovery of a bristle from deformation was measured by wrapping the wet bristle twice (angle 720) around a mandrel 0.111 inch in diameter, holding the bristle in this position for two minutes, releasing the bristle, and then measuring the angle retained, i. e., the angle of residual deformation (a), after the bristle had ceased to recover. The recovery is then determined by means of the following equation:

Recoveryin (720 a) X 100 720 The residual deformation is expressed by:

Deformation in To determine the percentage improvement in recovery exhibited by conditioned bristles over unconditioned bristles therefore, the values for a (angle of residual deformation for the conditioned bristles) and at (angle of residual deformation for unconditioned bristles) were substituted in the following equation:

(a'-a') X 100 a,

Both the above stiffness and recovery tests can be applied to either dry or wet bristles.

The wearing qualities or abrasion'resistance of the bristles was determined by making a brush from the dry bristles and then repeatedly passing the bristle side of the brush by mechanical means over a series of closely spaced glass rods. After two hours brushing" in this manner, during which time the brush made 5860 strokes over the glass rods, the brush was placed in water at 52 C. for 10 minutes, allowed to dry, and then examined to see how many bristles had been broken or deformed. The brushes were graded for bristledeformation by assigning values from to 5, where 0 represents no deformation and represents severe deformation. This test is a practical one and of interest in comparing the wearing qualities or durability of the bristles in comparison with other types of bristles. If desired, the glass rods used in the test may be coated with an abrasive material; thus in testing the suitability of bristles for use in tooth brushes, the rods were coated with tooth paste.

The invention will now be described in greater detail by means of the following specific examples:

EXAMPLE I A sample of viscosity stable polyhexamethylene adipamide derived from hexamethylene diamine and adipic acid and having an intrinsic viscosity of approximately 0.80 was formed into bristles as follows: The molten polymer was spun directly from the autoclave in which it had been prepared by extrusion at 290 C. under a pressure of 200 lbs. per sq. in., applied with oxygen-free nitrogen, through a spinneret having an 0.055 inch orifice attached to the bottom of the autoclave. Multiple orifice spinnerets can also be used. The filament was extruded at a rate of 120 ft. per minute into a bath of cold water placed 2.5 inches below the spinneret orifice. The filament obtained in this way had a diameter of approximately 0.023 inch. This filament was then soaked in water for 18 hours and cold drawn about 300%, i. e., until the length of the final oriented filament was about four times that of the original filament. Although the bristle obtained in this way was suitable for use in certain applications, its properties as indicated in Table I were improved by water or steam treatment. The data given in the table are for specimens of bristle which were given the following treatment while in a straight position: (1) aging under room conditions for three days (control); (2) soaking in water (about 25 C.) for three days; (3) steaming at atmospheric pres,-

. I g (maize sure for 15 minutes followed by three days soaking in cold water (about 25 (2.); and (4) soaking in .water at about 90C. for-one hour. After Table I E (modulus)Xl0" Recovery data (wet) Treatment 7 Residual Improve- Wet Dry deformament in tion recovery Percent Percent Aged in air 0. l3 0. 65 15 "0 Soaked in water 0. 2i 0. 65 12 1) Steam plus water n 0. 17 0. 51 5 67 Hot water 0. 17 0. 51 4 73 Pig bristle ('lientsin yellow string) 0. 3-0. 5 0. 8-1. 0 54 Standard.

EXAMPLE II Polyhexamethylene adipamide of intrinsic viscosity 1.02 was spun from melt directly from the autoclave in which it had' been prepared. The polymer was extruded at a'temperature of 290 C. under a pressure of 150 lbs. per sq. in., applied with oxygen-free nitrogen, through a spinneret orifice 0.07 inch in diameter attached to the bottom of the autoclave. The filament was extruded at a rate of 125'ft. per minute and was laid down on a moving endless belt which served to carry away the filament and support it during cooling. The resultant filament had a diameter of 0.035 inch. The filament was then subjected to steam at atmospheric pressure for 30 minutes to improve its drawing properties. The drawing operation was carried out by passing the filament directly from the steam chamber through a die having a diameter smaller than that of the original filament but larger than that of the completely cold drawn filament. Samples of the oriented bristle obtained in this way were then subjected to the treatments described in Example I with the average results indicated below in Table II.

In addition to having good stiffness and recovery, the polyamide bristles prepared and treated according to this invention have excellent wearing qualities. In an accelerated abrasion test of the type previously described, a tooth brush prepared from pig bristles lost about two thirds of its bristles, while a tooth brush containing polyamide bristles which had been treated with hot water according to the process of this invention lost no bristles and showed no wear (deformation 0 according to grading scale previously mentioned). In the same test a tooth brush containing untreated polyamide bristles lost no bristles but showed considerable wear (deformation 3). This improved resistance to stress of the polyamide bristles over pig bristles was also apparent during the fabrication of the brush for none of the polyamide bristles broke under the wedge which fastens the tuft in the handle,

whereas pig bristles gave considerable trouble in this respect. In the preparationof tooth brushes from polyamide bristles, I prefer to use bristles having diameters ranging from 0.005 to 0.02 inch.

From the foregoing description and examples, it will be evident to those skilled in the art that the present invention can be practiced in a number of ways. For most purposes, treatment with hot water (-100 C.) is most advantageous, for it is rapid in its eifect and gives a product of satisfactory stifiness and excellent recovery characteristics. Stiffness is a desirable property since it permits the use of smaller bristles. In view of the fact that stillness varies greatly with the diameter of the bristle, a product of any desired stiffness can be obtained by proper selection of bristle size. In some uses, e. g., shaving brushes, bristles of low stiffness are desired. In these and other uses, however, good recovery from deformation is important and for this reason the bristles should be given the treatment herein described.

In the practice of this invention the liquid water and steam treatments are not to be understood as superficial or casual treatments. To obtain the desired result the water treatment must be continued for a sufiicient time to improve the ability of the bristles to recover from deformation by at least 15 Casual water treatment does not give this result. This is clearly demonstrated by the fact that in actual use tooth brushes prepared from untreated polyamide bristles undergo much more rapid wear (deformation) than those prepared from treated polyamide bristles. The actual time required for the after treatment or conditioning which forms the basis of my invention will of course vary, depending on the diameter of the bristle and the temperature of the water but will usually be from about 0.2 to 75 hours. Hot or boiling water is rapid in its effect, being more rapid than steam itself. For bristles having a diameter between 0.01 and 0.04 inch, a cold water treatment of 20 to 60 hours is usually required, whereas 0.2 to 2.0 hours treatment with boiling water is usually suillcient. Steam treatment for bristles of this size generally requires slightly longer time than water at 85-100 C. As already indicated, steam treatment can be followed by a water treatment. The reverse procedure is also within the scope of this invention. The water and steam treatments should preferably be applied to the bristles while they are held substantially straight and under slight tension. After the treatment the bristles should be dried, i. e., brought to conditions of atmospheric temperature and humidity, in a straight position. This prevents the formation of a curl in the bristle. Of course, if a curled bristle is desired, the bristle shoud be held in a curled position during the treatment and For the preparation of the improved bristles of this invention, it is desirable to use polyamides having a melting point above C. and preferably above C. The polyamide, polyhexamethylene adipamide, cited in the foregoing examples has a melting point of about 263 C. under oiwgen-free conditions. A very useful class of polyamides for use in the preparation of the bristles of this invention are those derived from diamines of formula NHzCHaRCHzNH: and dicarboxylic acids of formula HOOCCHaRCHaCOOH and amide-forming derivatives of these reactants, R and R in said formulae representing divalent hydrocarbon radicals free from ethylenic and acetylenic unsaturation and R having a chain length of at least two carbon atoms. An especially useful class of polyamides within this group are those in which R is (CH2): and R is (CH2)y in which 2 is at least two and y at least one. As examples of polyamides falling within one or both of these classes might be mentioned polytetramethylene adipamide, polytetramethylene sebacamide, polypentamethylene sebacamide, polyhexamethylene betamethyl adipamide, polyoctamethylene adipamide, polydecamethylene adipamide, polydecamethylene p-phenylene diacetamide, and poly-p-iwlylene sebacamide. Polyamides derived from monoaminomonocarboxylic acids and their amide-forming derivatives may also be employed. As examples of such polyamides might be mentioned those derived from G-aminocaproic acid, 9-aminononanoic acid, and ll-aminoundecanoic acid. This invention is also applicable to bristles derived from a mixture of polyamides or from interpolymers or copolymers, i. e., polyamides derived from a mixture of polyamide-forming reactants, e. g., a mixture of two or more diamines with one Or more dicarboxylic acids, or a mixture of a diamine, a dicarboxylic acid, and an amino acid. As indicated in Example I, the polyamides employed may be viscosity stable, i. e., they can be prepared in the presence of an agent which brings about the formation of a polyamide whose intrinsic viscosity is not changed appreciably by heating at its melting point. Suitable viscosity stabilizing agents are described in Patents 2,190,770 and 2,174,527. The term intrinsic viscosity as used here is defined in these patents.

The invention is not limited to bristles composed solely of fiber-forming linear condensation polyamides. Such materials as plasticizers, melting point depressors, e. g., o-hydroxydiphenyl and diphenylolpropane, pigments, extenders, fillers, dyes, resins, oils, cellulose derivatives, disinfectants, antioxidants, bactericides, and the like may be present in addition to the polyamide.

If the foreign material is present in moderate amounts, it does not mask the desirable properties of the bristles. Pigments and dyes are particularly useful in preparing bristles having various degrees of luster and color. For example, valuable bristles can be prepared from polyamides containing a small amount (e. g., 0.01 to 5.0%) of a pigment-like material, such as titanium dioxide, zinc oxide, iron oxides, etc. Black bristles can be prepared with the use of carbon black.

That water should have such a remarkable effect on the properties of the oriented polyamide bristles is surprising in view of the fact that the polyamides are not very hygroscopic and have practically the same strength when wet as when dry. Furthermore, neither liquid water nor steam treatment of artificial bristles derived from cellulosie materials improves their properties, in fact, the bristles are warped by such treatments. It is further surprising that water at 85-100 C. should be more rapid in its action on polyamide bristles than steam.

This invention provides a simple and eonvenient method for preparing artificial bristles of unusually high qualities. The liquid water and/or steam after treatments of the oriented bristles, which comprise the important feature of this invention, give bristles which are superior to the large oriented polyamide filaments described in the previously referred to applications in recovery and wearing qualities. The improvement in recovery is frequently as much as 60%. So far as I am aware, these bristles are superior to any artificial or natural bristle that has previously been described, particularly in recovery and durability. A comparison has already been given of the properties of polyamide bristles with pig bristles, which are probably the highest grade bristles previously known. Further advantages which polyamide bristles have over pig bristles are that they can be prepared in any diameter and length, and can be made uniform throughout; pig bristles are thinner at one end than at the other. There is, therefore, much less waste in the case of the polyamide bristles. Furthermore, the polyamide bristles are more stable toward heat than the pig bristles.

The bristles of this invention can be used for a wide variety of purposes. They are particularly useful in preparing brushes which come in contact with water or chemical reagents, e. g., those used in tooth pastes. Thus, polyamide bristles are unaffected by 25 hours soaking in saturated sodium perborate solution, whereas pig bristles become discolored and lose their shape under this treatment. Excellent brushes of various types, e. g., paint brushes, hair brushes, tooth brushes, nail brushes, bottle brushes, dusting brushes, buffer or polishing brushes, etc., can be prepared from the bristles of this invention. In the preparation of brushes, etc., the polyamide bristles can be admixed with other types of bristles. The large filaments of this invention are also useful as fishline leaders, tennis strings, musical instrument strings, surgical sutures, mohair substitutes, horse hair substitutes, dental floss, rawhide substitutes, sewing thread, etc.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. A process for improving the recovery from deformation of oriented synthetic polyamide filaments which comprises subjecting the oriented filament-s while held in predetermined shape to treatment with liquid water at a temperature of at least 85 C. until the resulting filaments,

as compared with filaments of the same polywhich includes cold-drawing a filament formed from the polyamide, the step comprising treating the cold-drawn filament in a straight position with water at 85 to 100 C. until the resultant filament, as compared to a filament which has been oriented while wet but which has not been subjected to said water treatment after orientation, exhibits at least a 15% improvement in recovery from deformation, and drying said filament in a straight position.

4. In the manufacture of oriented filaments from fiber-forming synthetic linear polyamides which includes cold-drawing filaments formed from the polyamide, the step comprising treating the cold-drawn polyamide filaments while held'in predetermined shape with water at a temperature of at least 85 C. until the filaments are set in said shape.

5. A process for manufacturing bristles comprising forming a filament from a fiber-forming synthetic linear polyamide, soaking the filament in water, cold-drawing the filament .until it exhibits fiber orientation, and then further treating the filament while held in a straight positionwith water at a temperature of at least 85' C. until the filament is set in a straight position.

6. A process for manufacturing bristles comprising extruding a filament from a molten fiber-forming synthetic linear polyamide, rapidly chilling the filament, cold-drawing the filament until it exhibits fiber orientation, and then treating the filament while it is held straight with water at a temperature of at least 85 C. until the filament is set in a straight position.

"I. The process set forth in claim 1 wherein said polyamide is the reaction product of a diamine and a substance of the class consisting of dicarboxylic acids and amide-forming derivatives of dibasic carboxylic acids.

8. The step set forth in claim 5 wherein said polyamide is the reaction product of a diamine and a substance of the class consisting of dicarboxylic acids and amide-forming derivatives of dibasic carboxylic acids.

9. The step set forth in claim 4 wherein said polyamide is obtainable from a diamine of the formula NI-IzCHzRCmNm and a dicarboxylic acid of the formula HOOCCHzR'CHzCOOH in which R and R are divalent hydrocarbon radicals and R has a chain length of at least two carbon atoms.

10. A process for improving the recovery from deformation of oriented synthetic polyamide filaments which com-prises subjecting the filaments to treatment with water at a temperature of at least 85 C. while maintaining the filaments under tension, and continuing the treatment with water until the filaments are set in shape.

11. The process set forth in claim in which the filaments are in the form of a fabric held under tension.

12. An article of manufacture comprising oriented synthetic linear polyamide filaments which exhibit improved recovery from deformation, said filaments being those obtainable by subjecting oriented filaments of said polyamide while held in predetermined shape to treatment with water at a temperature of at least 85 C. until the resulting filaments, as compared with filaments of the same polyamide which have been oriented while wet but which have not been subjected to said watertreatment after orientation, exhibit at least a improvement in recovery from deformation.

13. A tooth brush containing synthetic linear polyamide bristles which exhibit improved recovery from deformation, said bristles being those obtainable by subjecting oriented bristles of said polyamide while held in a straight position to treatment with water at a temperature of at least 85 C. until the resulting bristles, as compared with bristles of the same polyamide which have been oriented while wet but which have not been subjected to said water treatment after orientation, exhibit at least a 15% improvement in recovery from deformation.

14. A process for improving the resistance to wrinkling of fabrics comprising oriented synthetic linear polyamide filaments which comprises subjecting the fabric while held in predetermined shape to the action of liquid water at a temperature of at least 85 C. until the resulting fabric is substantially set in said shape.

15. A brush containing synthetic linear polyamide bristles which exhibit improved recovery from deformation, said bristles being those obtainable by subjecting oriented bristles of said polyamide while held in straight position to treatment with water at a temperature of at least 85 C. until the resulting bristles, as compared with bristles of the same polyamide which have been oriented while wet but which have not been subjected to said water treatment after orientation, exhibit at least a 15% improvement in recovery from deformation.

16. A surgical suture comprising a synthetic linear polyamide filament which exhibits improved recovery from deformation, said filament being that obtainable by subjecting an oriented filament of said polyamide while held in predetermined shape to treatment with water at a temperature of at least 85 C. until the resulting filament, as compared with a filament of the same polyamide which has been oriented. while wet but which has not been subjected to said water treatment after orientation, exhibits at least a 15% improvement in recovery from deformation.

17. A musical instrument string comprising a synthetic linear polyamide filament which ex-.

hibits improved recovery from deformation, said filament being that obtainable by subjecting an oriented filament of said polyamide while held in predetermined shape to treatment with water at a temperature of at least 85 C. until the resulting filament, as compared with a filament of the same polyamide which has been oriented while wet but which has not been subjected to said water treatment after orientation, exhibits at leasta 15% improvement in recovery from deformation.

18. The process set forth in claim 1 in which said polyamide is that derived from a monoaminomonocarboxylic acid.

PAUL R. AUSTIN.

- Certificate of Correction Patent No. 2,226,529. December 31, 1940.

' PAUL R. AUSTIN It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Page 2, second column, line 18, f0

u I r n I (a 023x100 read (a 3x100 prfe 3, first column, line 52, in the table, fourth column thereof, for Residual de ormaread Residual defamation; and second column, line 67, for shoud read should; line 73, for warns reamigarns; page 5, first column, line 40, claim 8, for the claim reference numeral 5 re 4; line 45, claim 9, for 4 read 3; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 18th day of February, A. D. 1941.

HENRY VAN ARSDALE,

Acting Commissioner of Patents.

4 I Certificate oi Correction Patent No. 2,226,529; December 31, 1940.

PAUL R. AUSTIN It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Page 2, second column, line 18, for.

(a' a3 X100" read (a' -:),X100

p e 3, first column, line 52, in the table, fourth column thereof, for Residual dgfiumar read Residual defamation; and second column, line 67, for shoud read should; line 73, for wams" read arm; page 5, first column, line 40, claim 8, for the claim reference numeral 5 read 4; line 45, claim 9, for 4 read 8; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 18th day of February, A. D. 1941.

[SEAL] HENRY VAN ARSDALE,

Acting Commissioner of Patents. 

